The present invention relates to broadband (wideband) wireless (radio) access systems, in particular, to a method of simplifying the IP address configuration (establishment) procedures when a mobile/fixed terminal in idle mode changes to receiving mode or when performing handover.
In general, in a broadband wireless access system, an idle mode for a mobile (or fixed) terminal (e.g., mobile station, mobile subscriber station (MSS), user terminal, user equipment (UE), etc.) is supported in order to minimize power consumption. In idle mode, a ‘paging zone’ is defined as the entire region that is handled by a plurality of bases station called a ‘paging group’ and all base station included within the same paging zone have the same paging cycle value (Paging_Cycle) and paging offset value (Paging_Offset).
The terminal may request to the base station for changing into idle mode, and the base station delivers its paging zone identification (Paging-group ID) and the paging cycle and paging offset associated thereto to the terminal to allow that terminal to change into idle mode state. During the idle mode, the terminal can determine whether to maintain or end its idle mode based upon the paging that is delivered in broadcast format from the base station at each paging period.
Additionally, when there is traffic (e.g., data, packets, etc.) that needs to be delivered by the terminal in idle mode, the terminal may end its idle mode at any time. Also, when a terminal in idle mode does not receive paging within a set period of time due to reasons such as moving into another paging zone, losing synchronization, etc., then the terminal ends its idle mode.
When data traffic to be delivered to the terminal in idle mode is generated, the base station can make the terminal end its idle mode through paging. In such situations when traffic to be forwarded is generated for the terminal, the base station delivers an action code to enter network.
In this situation or when the terminal has data to be sent on the uplink, the terminal performs IP address configuration (establishment) procedures. If the network prefix used by the base station that received the paging did not change and remains the same, the above procedures could be omitted, but such omission is not possible because a procedure for performing network prefix comparison is not provided by the related art.
The idle mode can be comprised of the following operations and steps.                start idle mode by mobile terminal        cell selection        synchronization of paging message broadcast time of terminal        terminal paging unavailable cycle        terminal paging listening period        base station paging broadcast message transmission period        base station broadcast message        end paging available mode        
Among these, the technique related to the present invention is the base station paging broadcast message.
The base station paging broadcast message is a message sent via the base station or a different network element for informing a particular mobile terminal that currently delayed downlink traffic exists. This paging broadcast message must be transmitted through a broadcast connection identifier (CID) during a base station paging broadcast message transmission time period, and should be transmitted during the transmission time period regardless of the number of mobile terminals that require paging.
The base station paging broadcast message should be able to include one or more paging group IDs that indicate the logical classification of the base station that transmits. Regarding the base station paging broadcast message, the mobile terminals are distinguished by the mobile terminal MAC address hash, and a single base station paging broadcast message can include a plurality of MAC addresses.
The base station paging broadcast message must transmit an action code with respect to each mobile terminal that is distinguished by mobile terminal MAC address hashes, and such action codes are as follows.                00: no action required        01: perform Ranging to configure location and acknowledge message        10: perform initial network entry        11: reserved        
Among the above action codes, the base station paging broadcast message that is transmitted when there is downlink data, transmits an action code ‘10’ and the terminal performs network entry procedures based upon this action code.
Accordingly, in the related art, the mobile terminal must always re-configure (re-establish) its IP address when the mobile terminal in idle mode receives paging from the base station because there is downlink data to be received or when there is uplink data to be sent.
Namely, when a mobile terminal operating in idle mode moves into a different base station region and receives from the base station a paging broadcast message indicating that currently set aside (delayed) downlink data exists, the mobile terminal may omit the IP address configuration (establishment) procedures if the IP Subnet, Prefix, and Access Router (NetID) used by the base station are the same as those previously used by the mobile terminal. Also, when the mobile terminal in idle mode performs registration procedures with the base station because it has data to be sent on the uplink, the base station compares the previously received IP Subnet, Prefix, and Access Router (NetID) used by the mobile terminal with the IP Subnet, Prefix, and Access Router (NetID) that are can be used or are currently being used within the base station, and informs to the mobile station as to whether IP address re-configuration (re-establishment) is needed or not.
However, because the related art does not provide the procedures that can compare the IP Subnet, Prefix, and Access Router (NetID), the mobile terminal had to perform IP address configuration (establishment) procedures each time the idle mode was ended when there was uplink or downlink data, thus causing the problems of unnecessary time delays.
Meanwhile, the process for handover in a broadband wireless access system comprises a pre-processing procedure, a handover procedure, and a ‘drops and corrupted HO attempts’ procedure.
1. Pre-Processing Procedures for Handover
As the pre-processing procedures for handover of IEEE 802.16e, a procedure of informing the mobile terminals by broadcasting from a base station, the information related to neighboring base stations (e.g., Network Topology Advertisement), a procedure of measuring the channel quality of neighboring base stations based upon such information (e.g., MSS scanning of neighbor BS), and a procedure of selectively matching time differences and the like for the neighboring base station and initial terminal power value, as well as for synchronization (e.g., association procedures).
* Network Topology Advertisement
The base station informs all mobile stations within a cell about the information of neighboring base stations by transmitting information related to network constitution information in a broadcasting manner through a MOB_NBR-ADV MAC (Medium Access Control) message.
* MSS Scanning of Neighbor BS
As a mobile terminal must scan (search) neighboring base stations for handover, a scanning interval is requested to the base station through a MOB_SCN-REQ MAC message for scanning neighbor base stations, and the base station transmits a MOB_SCN-RSP MAC message in response to allocate an interval that allows the terminal to scan neighboring base stations. Also, the base station may directly transmit a MOB_SCN_RSP MAC message without any request of the mobile terminal (i.e., unsolicited request). At this time, the scanning interval and offset unit to start scanning that the base station allocates are all allocated in units of frames.
* Association Procedure
The association procedure is a procedure in which the terminal normally joins a cell by performing a ranging procedure with the base station. The associate procedure is performed when the terminal scans the base stations and selects a new base station. A RNG-REQ MAC message is transmitted by the terminal, and the base station transmits a RNG-RSP MAC message to set the power offset value, timing offset value, etc. to the appropriate values.
Transmitting of the RNG-REQ MAC message is referred to as an initial ranging operation, and is one of the most basic operations of an IEEE 802.16 system by which the terminal performs a network entry process. The target base station that receives a new terminal through handover (HO), transmits the matters in association to the cell of the terminal to the serving base station that the terminal was previously a part of, and then stores the information related to the terminal.
2. Handover (HO) Process
Based upon the neighboring base station and channel quality information obtained from the above handover pre-processing procedures, the terminal begins handover.
* Cell Selection
The cell selection operation is an operation of changing a cell in order to newly register with a base station that allows reception of a signal having a better Signal-to-Interference-Noise Ratio (SINR) than the SINR of the signal transmitted from the base station of a current cell before the terminal normally registers with the cell. At this time, the base station has no way of knowing about any movement of the terminal because the terminal has not yet performed any registration procedures.
* HO Initiation
Handover initiation can be performed by either the base station (BS) or the mobile terminal (MSS: mobile subscriber station). Namely, when the base station requests handover, it transmits a MOB_BSHO-REQ MAC message, and when the mobile terminal requests handover, it transmits a MOB_MSSHO-REQ MAC message. If the terminal transmits a MOB_MSSHO-REQ MAC message, the SINR of the signals received from neighboring base stations is transmitted to the base station, and the candidate base stations that can be a target base station during handover are transmitted to the currently serving base station.
The base station receives a MOB_MSSHO-REQ MAC message from the terminal or before the base station itself transmits a MOB_MSSHO-REQ MAC message in order to handover the terminal, the handover of the terminal is allowed after checking the responses (ACK) from neighboring base stations for performing handover of the particular terminal. The terminal or base station that receives the MOB_BSHO/MSSHO-REQ message transmits a MOB_MSSHO/BSHO-RSP MAC message to inform about the target base station that will perform the handover.
* HO Cancellation
After the MOB_MSSHO/BSHO-REQ MAC message is transmitted to allow the terminal or base station to perform handover, the terminal may cancel the handover. Here, the terminal can set a particular field of the MOB_HO-IND MAC message (e.g., HO_Type=01) and transmit such to the base station for canceling the handover that is currently being performed.
* Termination with the Serving BS
By transmitting a MOB_HO-IND MAC message to the serving base station, the terminal informs that handover has been properly completed and finishes the handover operation. Here, the terminal can set a particular field of the MOB_HO-IND MAC message (e.g., HO_Type=00) and transmit such to the serving base station to inform that handover has been properly completed. Upon receiving the MOB_HO-IND MAC message from the terminal, the base station terminates the MAC state machine, ARQ connection, and all connections related to data transmission that were allocated the terminal that has been handed over.
* HO Rejection
The terminal may reject the handover recommended by the base station, and does so by setting a particular field of the MOB_HO-IND MAC message (e.g., HO_Type=10) and transmits to the base station. Upon receiving a rejection message from the terminal, the base station re-constitutes the target base stations and re-transmits a MOB_BSHO-RSP message to the terminal.
3. Drops and Corrupted HO Attempts
If the downlink data received from the base station cannot be reconstructed (recovered, decoded, etc.) or if a RNG-RSP MAC message (with respect to a RNG-REQ MAC message) transmitted to the base station after handover is not properly received and the limit on the number of times that the RNG-REQ MAC message can be transmitted to the base station is reached, the terminal terminates communication. In such case, the terminal re-performs the network entry procedures with the desired target base station to perform an operation for connection recovery.
* Re-Entry with the Target BS
The terminal that performed handover performs a new network entry operation with the target base station, and also performs handover procedures for re-entry with neighboring base stations as well. However, from the point of view of the base station, the re-entry is performed in the same manner as a regular network entry procedure.
* Synchronization with Downlink and Obtain Parameters
The terminal that performed handover detects the downlink signal of the target base station to form synchronization with the base station, and receives a MOB_NBR-ADV MAC message transmitted by the base station to determine the conditions of neighboring base stations. Also, the terminal performs the same procedures as in a regular network entry procedure, namely, the operations to receive the DL_MAP and DCD message are performed.
* Obtain Uplink Parameters
The terminal that performed handover, after obtaining the downlink parameters as described above, receives uplink parameters through reception of a UL_MAP MAC message, a UCD message, etc.
* Ranging and Uplink Parameters Adjustment
The terminal that performed handover attempts to perform ranging with the new base station. This ranging operation is one of the most basic operations in a IEEE 802.16 system, whereby a ranging operation of a competitive allocation method is performed through a ranging opportunity (i.e., an interval allowing transmission of a ranging message) that is allocated by the base station based upon the 48 bit length MAC address of the terminal itself. Through this ranging operation, the terminal receives a new basic ID and a primary management ID allocated from the target base station. This operation achieved as the terminal obtains the uplink parameters by receiving the Fast_UL_Ranging IE that is transmitted by being inserted into the UL_MAP MAC message transmitted by the base station.
Here, the ranging opportunity received for the above ranging operation is performed in a contention-free manner, unlike the initial ranging operation performed for regular network entry.
* MSS Re-Authentication
This is an authentication procedure for normal operation of the terminal, whereby an authentication procedure occurs by using a PKM (Private Key Management) protocol, while the existing security context performs the authentication procedure without any changes.
* Re-Register and Re-Establish Provisioned Connections
The base station is in a state by which the 48 bit MAC address if the terminal has already been received, and since the authentication procedure of the terminal was performed properly, the proper registration procedure of the terminal is performed. The terminal begins the registration process by transmitting a REG-REQ MAC message, and the base station transmits a REG-RSP MAC message to re-establish a provisioned connection of the terminal before handover, to allow proper IP service to be performed.
In general, IP re-configuration (re-establishment) is performed after the mobile terminal performs handover, and IP re-configuration (re-establishment) need not be performed if the IP subnet is the same. However, in the related art, this cannot be known and IP re-configuration (re-establishment) must be done each time the terminal moves. Namely, even if the previous IP address can be used without having to configure (establish) an IP address after the terminal performs handover (for example, when the IP subnet or foreign agent remain the same), IP address configuration (establishment) is always performed after the mobile terminal moves according to the related art.